1. Field of the Invention
The present invention relates to a pressure-swing adsorption type gas separator system which is suitable for carrying out a process of separating, for instance, oxygen gas and nitrogen gas from air.
2. Description of the Prior Art
One example of a pressure-swing adsorption type gas separator system in the prior art is schematically shown in FIG. 10. In this system, raw gas is intermittently fed to a plurality of adsorption vessels 41A and 41B each accommodating adsorbent. Refined gas thus passes from the adsorption vessels 41A and 41B. While the above-mentioned feeding of the raw gas is interrupted, the gas adsorbed by the adsorbent is desorbed from the adsorbent and exhausted. In this gas separator system, the directions of flows of gases are switched at a high frequency by switching valves 42A and 42B consisting of electromagnetic valves, pneumatically operable valves or the like.
Another example of a pressure-swing adsorption type gas separator system in the prior art, which was designed to separate air into its components, is schematically shown in FIG. 11. In this system, air to be processed is pressurized by an air pump 51. The air is then selectively introduced into an adsorption tower 53 or 54 (adsorption process) by means of a five-port electromagnetic valve 52. Thus, nitrogen in the air is adsorbed by nitrogen adsorbent within one adsorption tower, and concentrated oxygen gas 56 is collected via a check valve 55. On the other hand, the other adsorption tower 54 or 53 is placed in communication with an exhaust gas system 57, held at atmospheric pressure, via the five-port electromagnetic valve 52, and nitrogen adsorbed within the adsorption tower 54 or 53 is desorbed under a reduced pressure and is exhausted through the exhaust gas system 57 (reduced-pressure desorption-reproduction process). The switching between the pressurized adsorption process and the reduced-pressure desorption-reproduction process is effected by driving the five-port electromagnetic valve 52 by feeding an electric current to an electromagnetic coil. It is to be noted that the air pump 51 is driven by a motor 58, and this motor 58 is associated with a cooling fan 59.
However, the above-described gas separator systems in the prior art employ an electromagnetic valve having a large bore diameter necessary to allow for a high flow rate of the raw gas. This valve generates a large electromagnetic force. Alternatively, if a pneumatically operable valve is employed, the system is complex and control air (or pressure) becomes necessary. Furthermore, the above-mentioned electromagnetic valves cannot be expected to have a long life because they are required to operate at a high frequency.
Moreover, in the gas separator system shown in FIG. 11, the five-port electromagnetic valve, provided on the feed side of the adsorption towers, is controlled by a sequencer, a timer, a microcomputer or the like to switch over at predetermined time period. However, in this system, if a voltage should vary during operation, the output of the air pump would vary regardless of whether an A.C. motor or a D.C. motor is used. For instance, if the voltage should lower, the outlet pressure of the air pump would lower and the air fed to an adsorption tower would be reduced. The pressure in the adsorption tower could not be raised back up to a predetermined pressure within a fixed time, and the oxygen concentration of the product gas would be lowered.